Insulated cups and containers are widely used for serving hot and cold beverages and other food items. Such articles may be made from a variety of materials including polystyrene foam, double-walled containers, and multi-layered paper-based containers such as paperboard containers containing an outer foamed layer. Paper-based containers are often more desirable than containers made from styrene-based materials because paper-based materials are generally more amenable to recycling, are biodegradable and have a surface more acceptable to printing. However, multi-layered and multi-walled paper-based containers are relatively expensive to manufacture compared to polystyrene foam-based articles and often do not exhibit comparable insulative properties. Paperboard containers having an outer foam insulation layer are generally less expensive to produce than double-walled containers, but the outer surface is less compatible with printing.
Attempts have been made to improve certain properties of paper by incorporating expanded as well as unexpanded microspheres within the paper. For example, U.S. Pat. No. 3,556,934 to Meyer describes production of paper products for books, magazines, and the like wherein unexpanded microspheres are incorporated into a papermaking furnish which is then formed into a web and dried. The microspheres expand on drying to produce a sheet said to have improved stiffness and caliper. However, the '934 patent deals with relatively low basis weight paper not suitable for insulated container manufacture, makes no mention of use of the product in the manufacture of paperboard containers having insulative properties, and gives no teaching as to how such a product could be produced so as to enable use of the product in fabricating insulative containers such as cups and the like.
Accordingly, there continues to be a need for paper-based materials which have good insulative properties and which can be produced on a competitive basis with polystyrene foam-based articles.